This invention relates in general to the manufacture of structural members having desired shapes, such as components for use in vehicle frame assemblies. More specifically, this invention relates to an improved apparatus and method for applying a lubricating material to a workpiece, such as a closed channel structural member, to facilitate the performance of a subsequent deforming process so as to manufacture a vehicle frame component having a desired shape for use in such a vehicle frame assembly.
Many land vehicles in common use, such as automobiles, vans, and trucks, include a body and frame assembly that is supported upon a plurality of ground-engaging wheels by a resilient suspension system. The structures of known body and frame assemblies can be divided into two general categories, namely, separate and unitized. In a typical separate body and frame assembly, the structural components of the body portion and the frame portion are separate and independent from one another. When assembled, the frame portion of the assembly is resiliently supported upon the vehicle wheels by the suspension system and serves as a platform upon which the body portion of the assembly and other components of the vehicle can be mounted. Although separate body and frame assemblies of this general type have been widely used in the past, they are commonly used today primarily for relatively large or specialized use modern vehicles, such as large vans, sport utility vehicles, and trucks. In a typical unitized body and frame assembly, the structural components of the body portion and the frame portion are combined into an integral unit that is resiliently supported upon the vehicle wheels by the suspension system. Unitized body and frame assemblies of this general type are found in many relatively small modern vehicles, such as automobiles and minivans.
One well known example of a separate type of vehicular body and frame assembly is commonly referred to as a ladder frame assembly. A ladder frame assembly includes a pair of longitudinally extending side rails that are joined together by a plurality of transversely extending cross members. The cross members connect the two side rails together and provide desirable lateral, vertical, and torsional stiffness to the ladder frame assembly. The cross members can also be used to provide support for various components of the vehicle. Depending upon the overall length of the vehicle and other factors, the side rails of a conventional ladder frame assembly may be formed either from a single, relatively long structural member or from a plurality of individual, relatively short structural members that are secured together. For example, in vehicles having a relatively short overall length, it is known to form each of the side rails from a single integral structural member that extends the entire length of the vehicle body and frame assembly. In vehicles having a relatively long overall length, it is known to form each of the side rails from two or more individual structural members that are secured together, such as by welding, to provide a unitary structural member that extends the entire length of the vehicle body and frame assembly.
Traditionally, the various components of known vehicle body and frame assemblies have been formed from open channel structural members, i.e., structural members that have a non-continuous cross sectional shape (U-shaped or C-shaped channel members, for example). Thus, it is known to use one or more open channel structural members to form the side rails, the cross members, and other components of a vehicle body and frame assembly. However, the use of open channel structural members to form the various components of vehicle body and frame assemblies has been found to be undesirable for several reasons. First, it is relatively time consuming and expensive to bend portions of such components to conform to a desired final shape, as is commonly necessary. Second, after such bending has been performed, a relatively large number of brackets or other mounting devices must usually be secured to some or all of such components to facilitate the attachment of the various parts of the vehicle to the body and frame assembly. Third, in some instances, it has been found difficult to maintain dimensional stability throughout the length of such components, particularly when two or more components are welded or otherwise secured together.
To address some of the problems of open channel structural members, it has been proposed to form one or more of the various vehicle body and frame components from closed channel structural members, i.e., structural members that have a continuous cross sectional shape (tubular or box-shaped channel members, for example). This closed cross sectional shape is advantageous because it provides strength and rigidity to the vehicle body and frame component. Also, this cross sectional shape is desirable because it provides vertically and horizontally oriented side surfaces that facilitate the attachment of brackets and mounts used to support the various parts of the vehicle to the body and frame assembly. In some instances, the various parts of the vehicle may be directly attached to the vertically and horizontally oriented side surfaces of the vehicle body and frame assembly.
In the manufacture of vehicle body and frame assemblies of this type, it is known that the closed channel structural member may be deformed to a desired shape by hydroforming. Hydroforming is a well known process that uses pressurized fluid to deform a closed channel structural member into a desired shape. To accomplish this, the closed channel structural member is initially disposed between two die sections of a hydroforming apparatus. When the two die sections are closed together, they define a die cavity having a desired final shape. Thereafter, the closed channel structural member is filled with a pressurized fluid, typically a relatively incompressible liquid such as water. The pressure of the fluid is increased to a magnitude where the closed channel structural member is expanded or otherwise deformed outwardly into conformance with the die cavity. As a result, the closed channel structural member is deformed into the desired final shape.
Hydroforming has been found to be a desirable forming process because portions of a closed channel structural member can be quickly and easily deformed to acquire a complex cross sectional shape. In those instances where the perimeter of the closed channel structural member is not the same as the perimeter of the die cavity, the cross sectional shape of the closed channel structural member is changed during the hydroforming process. However, at least ideally, the wall thickness of the closed channel structural member should remain relatively constant throughout the deformed region. Hydroforming has also been found to be a desirable forming process because portions of a closed channel structural member can be quickly and easily expanded from a relatively small perimeter to a relatively large perimeter. In those instances where the perimeter of the closed channel structural member is somewhat smaller than the perimeter of the die cavity, not only is the cross sectional shape of the closed channel structural member changed during the hydroforming process, but the wall thickness thereof is decreased. However, at least ideally, the wall thickness of the closed channel structural member should decrease uniformly through the expanded region.
During the hydroforming operation, because the inner surface of the hydroforming die is typically shaped differently from the outer surface of the closed channel structural member, one or more discrete portions of the outer surface of the closed channel structural member will initially engage the inner surface of the hydroforming die prior to engagement by the remaining portions thereof. These initially engaging portions of the outer surface of the closed channel structural member may become frictionally locked in position at the points of engagement because of the outwardly directed forces generated by the high pressure hydroforming fluid. As a result, the remaining portions of the closed channel structural member are stretched from the initially engaging portions as the deformation of the closed channel structural member is completed.
Such stretching results in undesirable variations of the wall thickness variations throughout the perimeter of the closed channel structural member. These wall thickness variations can be particularly acute when the hydroforming operation not only deforms the perimeter of the closed channel structural member, but also expands the magnitude of the perimeter thereof. Further, these wall thickness variations can result in undesirable weaknesses in the formed closed channel structural member.
Such friction between the outer surface of the closed channel structural member and the inner surface of the die may have adverse effects on the structural member. To minimize any adverse effects of such friction, it is known to coat the outer surface of the structural member with a lubricant prior to hydroforming. The lubricant is typically sprayed or applied by other suitable means and allowed to dry at room temperature. This process often results in an undesirable non-uniform coating of lubricant. Thus, it would be desirable to provide an improved method for applying lubricating material to a closed channel structural member prior to hydroforming, wherein the lubricating material maintains a relatively uniform wall thickness throughout.